Translation Regulation by Cytoplasmic RNA-binding Proteins”

M. VERÓNICA BAEZ;; M. HABIF; L, LUCHELLI; C C LEISHMAN; G. L. BOCCACCIO

Universidad de San Pablo, Facultad de Medicina de Ribeirao Preto, Brasil.

Workshop; Recent Advances in Confocal Microscopy and Their Applications; 2007

Workshop: Recent Advances in Confocal Microscopy and Their Applications . Ribeirão Preto,  Octubre 2007  G. L. Boccaccio, orador. Translation Regulation by Cytoplasmic RNA-binding Proteins: Neuronal P-bodies containing the translational repressor Smaug1 are located at the synapse and respond to synaptic stimulation. M. V. Baez; M. Habif; L. Luchelli; C. Leishman and G. L. Boccaccio. Instituto Leloir and FCEyN-UBA, Buenos Aires, Argentina.  Stress Granules (SG) and Processing Bodies (PB) are recently described mRNA-silencing foci. These related structures are present in the cytoplasm of eucaryotic cells as numerous and dynamic granules of variable size, usually between 0.1 to 10 um (Thomas et al., MBC 2005). While SG are transiently induced during the stress response and contains abortive translation initiation complexes, PB are constitutive, contains mostly de-adenylated mRNAs and includes molecules involved in mRNA decay as well as in translational repression. We have previously shown that mammalian Smaug1, -like the previously described Drosophila homolog- is a translational repressor of messengers carrying a specific RNA motif, the Smaug Recognition Element (SRE), both molecules forming foci related to SG and PB in transfected cell lines (Baez and Boccaccio, JBC 2005). We found that in mature neurons, a subset of neuronal P-bodies located in the dendrites contains the translational repressor Smaug1, whose expression coincides with the appearance of synaptic markers. Both in neurons and in transfected cells, Smaug1 foci are plastic and in equilibrium with the active translational apparatus, the granules dissolving when polysomes are stabilized pharmacologically. Relevantly, Smaug1 foci located at synapses disassemble upon depolarization and subsequent synaptic stimulation, known to trigger local translation at the post-synaptic region. These observations suggest that Smaug1 foci relaxation underlies the release of previously silenced mRNAs. siRNA-mediated gene silencing of the PB components Hedls/Ge-1 or RCK/p54/Me31B/DDX6, known to be required for PB integrity, resulted in marked decrease of hSmaug1-ECFP foci formation in transfected cell lines. Our studies underscore a novel pathway for mRNA regulation at the synapse involving Smaug1 and P-bodies. This hypothesis and whether Smaug1-mediated repression is controlled by synaptic activity remain to be investigated. Supported by NIH (USA); University of Buenos Aires, ANPCyT and CONICET (Argentina).